KR100618165B1 - Electrolytic method of and compositions for stripping electroless nickel - Google Patents

Abstract

Electrolyte stripping solutions containing novel uses of oxo acids and / or oxoates and hydrogen peroxide are formulated for rapid removal of electroless nickel from iron, steel, aluminum and titanium alloys as well as other selectable electrically conductive substrates. do. These materials provide improved resistance to etching of the substrate and can be formulated without chelating compounds, chromates, nitrates or concentrated acid solutions, thus enhancing worker safety and reducing the disposal costs of spent stripping solutions. You can.

Description

Electrolytic method of and compositions for stripping electroless nickel

The present invention relates to an electropeeling method and mixtures for peeling electroless nickel from a substrate. The electropeeling method can be described as the inverse of electroplating. Whereas electroplating is the application of a metal film to a substrate, electropeeling removes the film from the substrate. In electrolysis, the film dissolves by binding to negative ions in a bath that is attracted to its surface by a positive potential. The purpose of the stripper is to remove the film without damaging the lower substrate, but most of the anodic reactions do not distinguish between the film and the substrate and cause etching of the substrate.

Electroless nickel is difficult to attack because it is a strong chemical resistant film. An example of the chemical resistance of electroless nickel is the "nitric acid drop test". A drop of concentrated nitric acid is applied to the surface of the electroless nickel film. If any etching occurs within a given time, the test fails. The discovery of relatively mild chemicals and methods that can quickly remove these strong chemical resistant films has enormous economic value. This is more desirable if the peeling method can be made environmentally friendly and safe to be used for the restoration of incompletely plated parts.

Since the invention of autocatalytic chemical nickel deposition (now commonly referred to as 'electroless nickel plating'), the excellent chemical resistance of the laminate has been widely used to protect various preparations. This chemical resistance has been improved with innovative materials that have modified the laminate's structure over the years, making it more resistant to chemical attack. However, it has become increasingly difficult to remove only the electroless nickel while keeping the substrate intact.

Attempts to strip electroless nickel while varying success have been used in a variety of ways. One of the first methods attempted was an electrolytic stripper commonly used to strip electrolytic nickel. The release agent was prepared from concentrated sulfuric acid using a reverse current. Generally, the peeled part is immersed in the peeling solution tank and connected to the positive lead of the DC power supply (anodic). The current is traversed to a cathode electrode (cathode) made of lead or graphite. In the case of a method using the passivity principle, that is, when nickel deposits are dissolved by the action of sulfate ions, unlike nickel, the chemical properties of the steel substrates attack steel passive in the presence of highly concentrated sulfuric acid. Allow oxygen to be generated. This method failed when attempted to exfoliate most of the electroless nickel stacks because it was only steel, and the electroless nickel became passive.

Cunningham describes an electrical nickel stripper composed of concentrated sulfuric acid, chromic acid and hydrogen peroxide. This material was claimed to remove not only nickel but also chromium from ferrous substrates. Although this patent mentions that the material exfoliates electroless nickel stacks, it has the disadvantages of high processing cost of chromium and sulfuric acid content with its great risk, and the addition step to remove the oxide layer from the substrate before replating. Should be attempted.

Other chromic acid based nickel nickel release agents are described in US Pat. No. 4,647,352 (Cook). In this patent, a combination of chromic acid, phosphoric acid and sodium disulfide can be used to electrically peel off the electroless nickel. However, this material has a problem of sensitivity to the introduction of sulfate ions into the solution bath, requiring the use of barium carbonate treatment, which causes etching of the substrate. The treatment of the spent stripping baths is also very expensive due to the high chromic acid content.

U.S. Patent No. 4,664,763 (McMullen et al.) Employs incompletely plated portions of either or both of an anode and a cathode of an electrolytic stripping cell to strip nickel films. It discloses a water-soluble peeling solution containing chromic acid to apply. Electrolytic nickel films and electrolytic nickel films are said to be peeled off by this method. This stripping method cites several selective etch inhibitors, such as potassium iodide, to help prevent etching of the substrate. However, this method suffers from problems of etching and expensive processing of high content of chromic acid.

Other electrolytic methods usually use nitrates, such as ammonium nitrate or sodium nitrate, at a concentration of about 3 pounds per gallon. These methods use reverse direct currents to remove electroplated nickel and some low content of electroless nickel deposits from iron and steel. As the nickel dissolves, abrupt pH changes occur in the stripping solution tank causing a large amount of sludge problems. Sporadic passivation of large areas of unstripped nickel occurs as the exposed metal floats under the influence of current due to incompletely peeled portions. This problem is more evident when attempting to peel off the electroless nickel laminate containing about 7% or more of phosphorus.

Immersion nickel strippers (no current required) were supplied with cyanide compounds to the soluble nitrobenzene compounds in the solution bath to strip the nickel deposits. These strippers are known to be of limited use to strip electroless nickel containing low phosphorus, such as 1-7%, and electroless nickel laminates containing higher amounts of phosphorus are not stripped or impractical. It peels off at low speed. In addition to controlling contamination, the use of cyanide becomes increasingly expensive as the processing burden increases.

Nickel stripping solution baths using water-soluble nitrobenzene compounds have a wide range, such as any of ammonia and ammonium salts or ethylenediamine and / or their equivalents. These baths work well on electrolytic nickel stacks, while some low phosphorus electroless nickels achieve a peel rate of about 0.001 inches per hour, while high phosphorus electroless laminates average on an hourly basis. Proceed with slow removal of less than 0.0003 inches. Proper disposal of this type of stripping bath is very expensive because of their toxicity and high chelating power. These baths are adjusted to about 160-190 ° F. to remove the electroless nickel films and are very susceptible to thermal chemical decomposition as well as loss of volatile chemicals by heat.

US Pat. No. 4,554,049 to Bastenbeck discloses immersion nickel release agents using sulfamic acid, hydrogen peroxide, nitrates and chlorides. This patent claims to peel off electroless nickel (less than 7%) containing low amounts of phosphorus, but cannot efficiently peel off laminates containing high amounts of phosphorus.

U.S. Patent No. 4,720,332 (Coffey) discloses a reverse current for the rapid removal of soluble nitrobenzene compounds, zwitterions (as chelating agents), sulfide forming compounds, carbonates and electroless nickel stacks. Disclosed is a nickel stripping solution tank using the use. This method works well by removing the electroless nickel quickly (more than 0.002 inches per hour), while sometimes finely etched in high high current density areas to blunt the high gloss surfaces.

It is therefore an object of the present invention to improve the exfoliation technique of electroless nickel by providing a material for electrically exfoliating electroless nickel laminates containing low content and high content of phosphorus with equivalent high efficiency and ease.

It is also an object of the present invention to provide materials for electrically stripping electroless nickel, which have an improved resistance to etching of the substrate.

Another object is to remove chelates, nitrates, chromates, cyanide and high concentrations of acid solutions to provide a choice of alternative release agents that are safer and more environmentally friendly for use in the workplace.

Another object is to provide materials for stripping electroless nickel from electrically laminated polished nickel, electrically stacked sulfamate nickel and high content nickel alloys with little damage to the substrate and Provide methods.

Electrolytic stripping baths of the present invention consist of oxoacids and / or oxoacid salts, and hydrogen peroxide. It has been found that electroless nickel laminates can be dissolved in the anode of an electrolytic solution bath containing oxo acids and / or oxoacids and hydrogen peroxide. Substrates made of iron, cast iron, steel alloys, stainless steels, and titanium have a molar ratio of hydrogen peroxide / acid to one ionizable hydrogen. When maintained above a minimum suitable molar ratio of about 3.75 for strong oxoacids with and about 7.5 with strong oxoacids with two or more ionic hydrogens, it is protected from attack upon electrolysis. When weak oxo acids combine with weak oxoates to form a solution bath, lower peroxide / oxo acid ratios of as low as 1.5 may also be used. To prevent attack to aluminum substrates only by sulfuric acid and sulfamic acids and / or salts thereof, they may be selected from strong oxo acids, and weak oxo acids and / or exhibit affinity with certain hydrogen peroxides. Salts may be used. When stripping electroplated nickel, cast nickel, kovar (kovar, iron, nickel, cobalt alloy) and nickel sulfamate from the substrates, only weak oxo acids and / or combinations of oxoacids should be used.

In order to achieve the objects of the present invention, a strong acid is contemplated wherein the acid has a dissociation constant K ₁ greater than about 2 × 10 ⁻¹ . Examples of strong oxo acids are sulfuric acid, nitric acid, sulfamic acid, alkyl sulfonic acid, aryl sulfonic acid and monoalkyl esters of sulfuric acid. of sulfuric acid).

Examples of weak oxo acids are phosphoric acid, pyrophosphoric acid, alkyl phosphoric acid, glucophosphonic acid, oxalic acid, formic acid, propanoic acid ( propanoic acid, bis methanol propanoic acid, acetic acid, butanoic acid, benzoic acid, phthalic acid, citric acid, tartaric acid ), Malic acid, malonic acid, maleic acid, maleic acid, butyric acid, succinic acid, glycolic acid, glutaric acid, glutaric acid Gluconic acid, adipic acid, boric acid, ethylenediaminetetraacetic acid and its equivalents, nitrilotriacetic acid, amino acetic acid and Polyvinyl sulfonic acid.

The concentration of hydrogen peroxide applied in the present invention may be about 1% to about 99%, but a concentration of about 8% is preferred. While maintaining the minimum molar ratios of peroxide / oxo acid disclosed, the oxo acid and / or oxoacid salts can vary from 0.01 mole / liter to saturated.

The pH range for the practice of the present invention is about 0-8, the more preferred pH range is about 1-7, the most preferred range is about 1.5-4.5.

Oxygen-free halogen acids (hydrofluoric acid and hydrochloric acid) are suitable peroxide / hydrogen peroxide that can prevent attack on iron or steel substrates when these acids and / or their salts are used in an amount of about 0.1 mol / l or more in the stripping bath. Since there is no proportion of acid, it is excluded from the present invention. Iodic acid, bromic acid and chromic acids and / or salts are excluded due to incompatibility with hydrogen peroxide when mixed with hydrogen peroxide or during the stripping process.

The present invention utilizes stripping solution baths consisting of oxo acids and / or oxoacids and hydrogen peroxide, whereby electroless nickel laminates are electrically stripped from substrates of iron, cast iron, steel alloys, stainless steel, aluminum and titanium. Discuss what can be done. Surprisingly, electrically laminated nickel, cast nickel, kovar and high nickel content alloy substrates can peel electroless nickel stacks without significant substrate attack by stripping baths of weak oxo acids and / or oxoates. have. In addition, the electroless nickel can be stripped from aluminum substrates without a significant attack on the substrate if the strong oxo acids and / or strong oxoacid salts are selected from sulfuric acid and salts thereof and / or sulfamic acid and salts thereof. have. Weak oxo acids and / or oxoacids that are friendly with hydrogen peroxide may also be used to strip the electroless nickel from aluminum. If the molar ratio of hydrogen peroxide / oxo acid is maintained at least about 3.75 or more for strong oxo acids with one ionizable hydrogen, and the molar ratio of hydrogen peroxide / oxo acid for strong oxo acids with two or more ionizable hydrogens is about If kept at 7.5, the metals are protected from attack during electrolysis. When weak oxo acids and / or weak oxoates combine to form a stripping solution bath, a low peroxide / oxo acid ratio of about 1.5 can be used.

Oxygen-free halogen acids (hydrofluoric acid and hydrochloric acid) have no suitable concentration of hydrogen peroxide that can prevent the attack of iron, steel alloy, and aluminum substrates when these acids are present at concentrations of about 0.1 mol / l or more, Excluded from the present invention. In the case where a relatively large amount of oxoacid ions is involved in the solution bath, extremely small amounts of halogen ions cannot attack the substrate. For example, the amount of chlorine ions caused by chlorination of drinking water does not affect the substrate, but when the concentration of chlorine ions increases to about 1 mol / l or more, partial attack of the substrate may occur.

Considering practical situations such as solution conductivity and operator safety, about 5-20% by volume of hydrogen peroxide (10-40% by volume with 50% hydrogen peroxide) is the preferred operating range, and 7-10% by volume of hydrogen peroxide (50% 14-20% by volume of hydrogen peroxide) is the most preferred range of action. By using an appropriate molar ratio of hydrogen peroxide to this range of hydrogen peroxide concentration, it is possible to exfoliate at current densities of about 100 amps / sq.ft. Without realistic considerations such as worker safety and waste considerations, there is no limit to the maximum concentration for hydrogen peroxide.

The concentration of oxo acid and / or oxoacid salts may vary over various ranges as long as the minimum molar ratios of peroxide / acid are maintained. Acids and / or salts may vary from 0.01 mol / l to saturation. However, since the current flowing through the solution bath determines the amount of nickel peeled off for a certain period, it is preferable that the peeling solution bath has a low electrical resistance. Thus, the selection of the amount and type of oxo acids and / or oxoates that increase the conductivity of the solution is very important for the fast and economical removal of the electroless nickel film.

The preferred temperature range for controlling the stripping bath of the present invention is about 60-115 ° F., and the most preferred temperature range is about 80-100 ° F. Of course, lower or higher temperatures may be used, but lower conductivity and solubility occur at lower temperatures, and accelerated peroxide decomposition may occur at higher temperatures.

The following examples are merely to aid the understanding of the present invention, but do not limit the scope of the present invention.

Example 1

Since the following solution baths are not chelated, the disposal of the spent peeling solution bath of this formulation is simple and inexpensive. It is used very safely because it contains only about 3 times the acetic acid content of conventional vinegar. The peroxide content is high enough to bleach hair, but not so high that it poses a serious danger to workers.

Chemical content

Monosodium phosphate 20g

20 ml of acetic acid (68%)

25 ml of hydrogen peroxide (50% by volume)

Water to fill with 140 ml of total volume (tap water)

Molar ratio of peroxide / acid: 1.82

The chemicals were dissolved to prepare a total of 140 ml of solution. The temperature of the solution was adjusted to 90 ° F. 2.1 inch wide stainless steel cathodes were placed in the solution on either side of the beaker containing the solution and connected to the negative side of the variable voltage DC power supply. A 1 inch wide mild steel panel plated with electroless nickel containing 0.001 inch of about 12% phosphorus is suspended in the beaker center between the two stainless steel cathodes. The plated panels were connected to the positive side of the power source. To prevent layering of the solution, a stir bar of TEFLON ^® (polytetrafluoroethylene) coating was placed in the beaker and used to stir the solution slowly. Current was applied and the voltage drop across the stripping solution was adjusted to four. After instantaneous bubbles were formed in the plating, nickel began to dissolve in the stripping bath and all foaming at the anode was stopped. Initial current was 0.75 amps. After about 30 minutes, the steel-based metal began to be exposed at an angle of 90 degrees below the plated portion. Unlike nitrate-based electrolytic release agents, the exposed steel substrate is not gas. The electroless nickel film continued to dissolve, shrinking from all sides of the panel and becoming parabolic as it decreased. When the residual area coated with electroless nickel was about 30% of the panel area exposed to the solution, gas evolution began slowly from the metal. After about 45 minutes, the electroless nickel did not remain on the panel. An additional 15 minutes is the time to confirm complete delamination and to see if any etching occurs in the steel panel. Etching did not occur. Mild steel panels were only polished if they were first immersed in an electroless nickel plating solution.

Aluminum test panels were also peeled off with equally good results in this solution.

The following examples are constructed in accordance with Example 1 and show various oxo acids and / or oxoacids that may be used in the present invention.

Example 2

Chemical content

12 g sodium hydrogen sulfate

15 g sodium sulfate

35 ml of hydrogen peroxide (50%)

Water to fill with 140 ml of total volume (tap water)

Molar ratio of peroxide / acid: 6.1

This bath had less resistance to the flow of current than Example 1, and the initial current was 1.02 amps at an initial voltage drop of 4 volts across the bath. The same panel as used in Example 1 peeled off with the same good results within about 30 minutes.

Example 3

Chemical content

Sulfuric acid (66 ⁰ Baume) 2.35 ml

35 ml of hydrogen peroxide (50%)

Water to fill with 140 ml of total volume (tap water)

Peroxide / acid molar ratio: 15.0

The solution bath was configured as in Example 1. The solution bath had very good conductivity. It was peeled off without visible attack from substrates made of steel, aluminum and titanium. 2.35 g of nickel was fed into the solution bath and show computationally 97.9% of the acid used to react with nickel. The additional use of this solution bath drastically raised the pH from pH 4.8 measured when the nickel content reached 2.35 g. Successive exfoliation caused precipitation of nickel hydroxide and rapid decomposition of hydrogen peroxide as the pH reached about 6-7.

Example 4

Chemical content

10 g citric acid

10 g sodium citrate

20 ml of hydrogen peroxide (50%)

Water to fill with 140 ml of total volume (tap water)

Molar ratio of peroxide / acid: 6.79

Excellent results have been obtained for substrates of steel, aluminum, titanium and cast iron.

Example 5

Chemical content

Ammonium Sulfate 14g

20 ml of hydrogen peroxide (50%)

Water to fill with 140 ml total volume

The solution bath exfoliated the electroless nickel without any obvious attack on the steel substrate, but the solution became turbid with nickel hydroxide as the pH rose to 6-7. Peroxide became more unstable as pH rose to 5.5 or more.

Example 6

Chemical content

15 g magnesium sulfate

25 ml of hydrogen peroxide (50%)

Water to fill with 140 ml total volume

The bath stripped the electroless nickel without attacking the steel, but the peroxide decomposition proceeded rapidly due to the high pH of 6-8 during the test.

Example 7

Chemical content

10 g sodium citrate

10 g citric acid

Hydrogen peroxide (50%) to fill with 140 ml total volume

Molar ratio of peroxide / acid: 44.4

This bath was used to test the upper limit of the hydrogen peroxide concentration. The solution worked well without any significant difference from that obtained in Example 4.

Example 8

Chemical content

15 g of sodium phosphate

10 g citric acid

20 ml of hydrogen peroxide (50%)

Water to fill with 140 ml total volume

Molar ratio of peroxide / acid: 7.4

This solution bath peeled off well at 60 amps / sq.ft. Partial heating of the solution was caused by battery resistance of the solution bath. The bath was stripped of 3.25 milliliters of electroless nickel for 1 hour 10 minutes. There was no attack on the steel substrate. No visible attack on steel or aluminum substrates was observed.

Example 9

Chemical content

10 g sulfamic acid

10 g of sodium phosphate-3

20 ml of hydrogen peroxide (50%)

Water to fill with 140 ml total volume

Molar ratio of peroxide / acid: 3.4

This bath was tested at 60 amps./sq.ft. No attack on steel, aluminum or titanium based metals was observed.

Example 10

Chemical content

10 ml formic acid

10 g of sodium formate

25 ml of hydrogen peroxide (50%)

Water to fill with 140 ml total volume

Molar ratio of peroxide / acid: 2.1

This solution bath showed excellent results of peeling nickel from steel, aluminum and cast iron substrates.

Example 11

Chemical content

10 ml of acetic acid (68% by volume)

10 g sodium acetate

20 ml of hydrogen peroxide (50%)

Water to fill with 140 ml total volume                 

Molar ratio of peroxide / acid: 3.1

This solution bath peeled about 10 times slower than the solution of Example 1 at 4 volts due to the low solution conductivity. The solution did not attack the steel substrate.

Example 12

Chemical content

10 g sodium sulfate

10 g of glutaric acid

22 ml of hydrogen peroxide (50%)

Water to fill with 140 ml total volume

Peroxide / acid molar ratio: 5.1

This solution bath dissolved 2.51 g of electroless nickel before the test was terminated at pH 4.4. No attacks on steel substrates were observed.

Example 13

Chemical content

5 g sodium chloride

10 ml of acetic acid (68%)                 

20 ml of hydrogen peroxide (50%)

Water to fill with 140 ml total volume

Molar ratio of peroxide / acid: 3.1

In the solution bath, the steel-based metal was etched due to the high chloride content.

Example 14

Chemical content

8 g sodium chloride

20 ml of acetic acid (68%)

20 ml of hydrogen peroxide (50%)

Water to fill with 140 ml total volume

Peroxide / acid molar ratio: 1.5

This solution bath peeled very well compared to the result of Example 13 and there was no etching for steel.

Example 15

Chemical content

Citric acid (MW = 210) 10 g                 

10 g sodium sulfate

30 ml of hydrogen peroxide (50%)

Water to fill with 140 ml total volume

Molar ratio of peroxide / acid: 11.1

This solution tank exfoliated 4.2 g of nickel which is a stoichiometric amount of citric acid in a solution tank. The pH of the solution began to rise sharply and the test was terminated. There was no attack on steel, aluminum, cast iron or titanium substrates.

Example 16

Chemical content

10 g maleic acid

22 ml of hydrogen peroxide (50%)

Water to fill with 140 ml total volume

Peroxide / acid molar ratio: 4.5

In the bath, good performance and reduced electrical conductivity were observed.

Example 17

Chemical content                 

Sulfuric acid (66 ⁰ Baume) 3 ml

Borax 12g

22 ml of hydrogen peroxide (50%)

Water to fill with 140 ml total volume

Molar ratio of peroxide / acid: 7.4

This solution bath was excellently peeled off. No attack on steel or aluminum substrates was observed. The high conductivity of the solution bath was confirmed. The solution bath was stripped to 100 amps / ft ² without visible attack on steel or aluminum substrates.

Example 18

Chemical content

10 ml glycolic acid (goods)

10 g sodium sulfate

22 ml of hydrogen peroxide (50%)

Water to fill with 140 ml total volume

Molar ratio of peroxide / acid: 2.9

This solution bath was excellently peeled off. No attack on steel or aluminum-based metals was observed.

Example 19

Chemical content

15 ml of phosphoric acid (85% by volume)

25 ml of hydrogen peroxide (50%)

Water to fill with 140 ml total volume

Molar ratio of peroxide / acid: 2.9

This solution bath was excellently peeled off. No attack on steel or aluminum based metals was observed.

Example 20

Chemical content

5 g of boric acid

10 g sodium sulfate

20 ml of hydrogen peroxide (50%)

Water to fill with 140 ml total volume

Peroxide / acid molar ratio: 4.4

The starting pH of this batch was 5.32. When the pH reached 5.84, precipitation began to form in the solution bath. The nickel content of the solution bath was 0.6 g. Nickel hydroxide precipitated, but peeling continued without attacking steel or aluminum.

Example 21

Chemical content

10 g sodium hydrogen sulfate

10 g of sodium pyrophosphate

25 ml of hydrogen peroxide (50%)

Water to fill with 140 ml total volume

Molar ratio of peroxide / acid 5.3

This solution bath exfoliated the electroless nickel excellently. No attack on steel or aluminum plated substrates was observed.

Example 22

Chemical content

15 g of citric acid

10 g sodium tripolyphosphate

25 ml of hydrogen peroxide (50%)                 

Water to fill with 140 ml total volume

Peroxide / acid molar ratio: 6.2

This solution bath showed excellent results peeling from electroplated nickel, cast nickel and cobar alloy.

Example 23

Chemical content

20 ml of acetic acid (68%)

15 g sodium nitrate

20 ml of hydrogen peroxide (50%)

Water to fill with 140 ml total volume

Peroxide / acid molar ratio: 1.5

This solution bath stripped the electroless nickel deposits with nearly 100% efficiency. No visible attack on the steel substrates was observed. The electrically laminated shiny nickel was slowly dissolved in the bath (oxygen dissociated on the nickel surface) because of the nitrate content.

Example 24

Chemical content

15 g of citric acid                 

Ammonium Nitrate 50g

25 ml of hydrogen peroxide (50%)

Water to fill with 140 ml total volume

Molar ratio of peroxide / acid: 6.1

This solution bath stripped the shiny electroplating nickel with low efficiency. That is, some gas generation occurred as the electroplating nickel was dissolved. However, electroless nickel laminates containing a high content of 12% phosphorus were stripped to nearly 100%. This material is an improvement over the prior art because, with the use of acid, the precipitation of nickel hydroxide does not rise to the point of pH which causes sludge of the solution which is lack of prior art nitrate electrolytic release agents. In addition, the nitrate-based material can peel off electroless nickel and polished electroplating nickel containing a high content of phosphorus without attacking steel or cast iron substrates with one peeling solution. Aluminum substrates were attacked.

Example 25

Chemical content

6 ml nitric acid (68% by volume)

20 ml of hydrogen peroxide (50%)

Water to fill with 140 ml total volume

Molar ratio of peroxide / acid: 3.7

This solution bath peeled off the shiny electroplating nickel, causing the generation of oxygen gas. It delaminated the electroless nickel very quickly because of its high conductivity. In this solution, the aluminum substrates were attacked, but the steel or titanium substrates were not attacked.

Example 26

The following example has a volume of 1 liter. This solution shows a very low peroxide / oxo acid concentration of 0.3 / 0.04 moles.

Chemical content

Sulfuric acid (66 ⁰ Baume) 2.3 ml

Hydrogen peroxide (50%) 17 ml

Water to fill with 1 liter of total volume

Molar ratio of peroxide / acid: 7.5

Its conductivity was reduced, but this bath stripped the electroless nickel containing 12% phosphorus without a visible attack on steel or aluminum test panels.

Example 27

Chemical content

9 ml of methanesulfonic acid

20 ml of hydrogen peroxide (50%)

Water to fill with 140 ml total volume

Molar ratio of peroxide / acid: 3.75

This solution bath had high conductivity. It peeled the electroless nickel from the substrates of steel, cast iron, titanium and cast nickel, without a visible attack on the substrate. Aluminum substrates were slowly attacked.

Example 28

Chemical content

14.8 g of benzene sulfonic acids

20 ml of hydrogen peroxide (50%)

Water to fill with 140 ml total volume

Molar ratio of peroxide / acid: 3.75

The results obtained were the same as those obtained in Example 27.

The following examples show the attack on the substrate due to low peroxide / oxo acid ratios.

Example 29

Chemical content

Sulfuric acid (66 ⁰ Baume) 5.4ml

20 ml of hydrogen peroxide (50%)

Water to fill with 140 ml total volume

Molar ratio of peroxide / acid: 3.75

A 1 inch wide uncoated steel test panel was immersed in the solution and immediately attacked before electrical connection was made to the test panel. The panel was replaced by another steel panel plated with 0.001 inch of electroless nickel. This panel was connected to the positive lead of the power supply as in Example 1, and the voltage was adjusted to 4 volts. Electroless nickel quickly dissolved due to its high current density. After the panel was peeled off the electroless nickel, the part was removed from the stripping solution tank and exploded with the stripping solution remaining on its surface.

Example 30

Chemical content

20 ml of acetic acid (68%)

10 g sodium sulfate

10 ml of hydrogen peroxide (50%)

Water to fill with 140 ml total volume

Peroxide / acid molar ratio: 0.77

The same unplated test panel as in Example 29 was immersed in the stripping solution bath without electrical contact. The test panel was attacked very slowly by the solution bath. As in Example 29, the panels were replaced with plated panels and peeled. When the panel was removed, the steel-based metal was attacked but its attack speed was not explosive. The addition of 15 ml of hydrogen peroxide (50%) to the solution stopped all etching and led to the same results as obtained in Example 1.

Although the present invention has been described in the most practical and preferred embodiments, it is not limited to the embodiments disclosed in the present invention. Conversely, various modifications are possible without departing from the spirit and scope of the claims.

Accordingly, modifications of the invention may be made without disclosure from the novel aspects of the invention as defined in the claims. All patents cited herein are hereby incorporated by reference in their entirety.

Claims (21)

A method of peeling electroless nickel laminates from a substrate selected from the group consisting of iron, cast iron, steel alloys, stainless steels, aluminum, plated nickel, cast nickel, iron / nickel / cobalt alloys, nickel sulfamate and titanium, The method, a) immersing a substrate comprising an electroless nickel laminate in a mixture comprising hydrogen peroxide and a compound selected from the group consisting of oxo acids, oxoacids and combinations thereof in an electrolytic bath; b) peeling off the electroless nickel stacks from the substrate by electrolysis; A molar ratio of hydrogen peroxide / acid of at least 3.75 is maintained for one ionizable hydrogen and strong oxo acids having a dissociation constant of at least 2 × 10 ⁻¹ , A molar ratio of hydrogen peroxide / acid of at least 7.5 is maintained for strong oxo acids with at least two ionizable hydrogens, For weak oxoacids with dissociation constants less than 2 × 10 ⁻¹ , the molar ratio of hydrogen peroxide / acid of at least 1.5 is maintained, If the substrate is aluminum and strong oxo acids in the mixture are used, the strong oxo acids are selected from the group consisting of sulfuric acid, sulfamic acid, their salts and combinations thereof, If the substrate is selected from plated nickel, cast nickel, iron / nickel / cobalt alloy and sulfamic acid substrates, electroless nickel laminates in which weak oxo acids, oxoates and combinations thereof are used in the mixture. Peeling method. The method of claim 1, wherein the strong oxo acids are selected from the group consisting of sulfuric acid, nitric acid, sulfamic acid, alkylsulfonic acid, arylsulfonic acid, and monoalkyl esters of sulfuric acid. The method of claim 1, wherein the weak oxo acids are phosphoric acid, pyrophosphoric acid, alkylphosphoric acid, glucophosphonic acid, oxalic acid, formic acid, propanoic acid, bismethanolpropanoic acid, acetic acid, butanoic acid, benzoic acid, phthalic acid, citric acid, tartaric acid, malic acid, In the group consisting of malonic acid, maleic acid, butyric acid, succinic acid, glycolic acid, glutaric acid, gluconic acid, adipic acid, boric acid, ethylenediaminetetraacetic acid and its equivalents, nitrilotriacetic acid, aminoacetic acid and polyvinylsulfonic acid Method for stripping electroless nickel laminates selected. The method of claim 1, wherein the hydrogen peroxide is present in the mixture at a concentration between 1 and 99% by volume. 5. The method of claim 4, wherein the hydrogen peroxide is present at a concentration of 8% by volume. The method of claim 1 wherein the compound selected from the group consisting of oxo acids, oxoacids and combinations thereof is present in the mixture at a concentration between 0.01 mol / l and saturation. The method of claim 1, wherein the mixture is maintained at a pH between 0 and 8. 8. The method of claim 7, wherein the mixture is maintained at a pH between 1.5 and 4.5. The method of claim 1 wherein the mixture is maintained at a temperature between 60 and 115 ° F. 10. The method of claim 9, wherein the mixture is maintained at a temperature between 80 and 100 degrees Fahrenheit. A mixture for electrolyseling electroless nickel laminates from a substrate, a) a compound selected from oxo acids, oxoacids and combinations thereof and b) contains hydrogen peroxide, A molar ratio of hydrogen peroxide / acid of at least 3.75 is maintained for one ionizable hydrogen and strong oxo acids having a dissociation constant of at least 2 × 10 ⁻¹ , A molar ratio of hydrogen peroxide / acid of at least 7.5 is maintained for strong oxo acids with at least two ionizable hydrogens, A mixture in which the molar ratio of hydrogen peroxide / acid of at least 1.5 is maintained for weak oxo acids with dissociation constants less than 2 × 10 ⁻¹ . 12. The mixture of claim 11 wherein the strong oxo acids are selected from the group consisting of monoalkyl esters of sulfuric acid, nitric acid, sulfamic acid, alkylsulfonic acid, arylsulfonic acid and sulfuric acid. The method of claim 11, wherein the weak oxo acids are phosphoric acid, pyrophosphoric acid, alkylphosphoric acid, glucophosphonic acid, oxalic acid, formic acid, propanoic acid, bismethanolpropanoic acid, acetic acid, butanoic acid, benzoic acid, phthalic acid, citric acid, tartaric acid, malic acid, In the group consisting of malonic acid, maleic acid, butyric acid, succinic acid, glycolic acid, glutaric acid, gluconic acid, adipic acid, boric acid, ethylenediaminetetraacetic acid and its equivalents, nitrilotriacetic acid, aminoacetic acid and polyvinylsulfonic acid Mixture selected. 12. The mixture of claim 11 wherein said hydrogen peroxide is present in said mixture at a concentration between 1 and 99% by volume. The mixture of claim 14 wherein said hydrogen peroxide is present at a concentration of 8% by volume. 12. The mixture of claim 11 wherein the compound selected from the group consisting of oxo acids, oxoacids and combinations thereof is present in the mixture at a concentration between 0.01 mol / l and saturation. 12. The mixture of claim 11, wherein the mixture has a pH between 0 and 8. 18. The mixture of claim 17, wherein the mixture has a pH between 1.5 and 4.5. delete The mixture of claim 11, wherein the mixture does not comprise chelating compounds, chromates or cyanide. delete